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Boiler > Boiler Midterm > Flashcards

Boiler Midterm Flashcards

1
Q

Define Boiler Horsepower

A

amount of energy equal to evaporation of 34.5 lbs of water / hr at a feedwater temperature of 212 degrees F

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2
Q

What is the max pressure of a Low Pressure Boiler?

A

15 psi

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3
Q

How does a Firetube Boiler operate?

A

hot gases of combustion travel through the tubes with water surrounding the tubes. Max pressure approx. 350 psi, BHP approx. 750 (HRT, Scotch Marine, Vertical Firetube).

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4
Q

What conditions would lead to a Boiler Explosion?

A

Sudden drop in pressure without a corresponding drop in water temperature. Water will flash into steam and expand 1600x, casing explosion

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5
Q

How do pressure and temperature correspond?

A

Temperature increases with pressure in enclosed vessel while saturated. Breakdown when steam becomes superheated

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6
Q

Define Thermal Efficiency

A

ratio of heat absorbed by boiler water (boiler output) to heat available in the fuel (boiler input)

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7
Q

Describe a Horizontal Return Boiler

A

Firetube boiler with shell suspended over firebox. Can use fuel oil, natural gas, coal, wood. Tube sheets supported by stays and diagonal stays

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8
Q

What are the advantages and disadvantages of of a vertical tube boiler?

A

one pass firetube, gases can’t be held in boiler with baffles (efficiency loss), less floor space needed, but larger ceilings needed

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9
Q

How does an Electrode Boiler operate?

A

Heat generated by current through boiler water because of conductivity

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10
Q

Why are Baffles used?

A

direct gases so they come into very close contact with Boiler Heating Surface for higher efficiency

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11
Q

What is the purpose of Waterwalls?

A

ser of tubes on furnace area of watertube boiler used to increase heat surface and extend life of refractory

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12
Q

Why are Superheaters used?

A

creates Dry Steam superheated without water which reduces moisture to protect process equipment and adds heat energy for more work

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13
Q

Where is the Open Feedwater Heater located?

A

Above the Feedwater Pumps for slight positive pressure on suctions side of pump

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14
Q

What is a Manual Reset Valve?

A

Electric valve on the main gas line of Low Pressure Boilers that can’t be opened until the pilot is lit

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15
Q

What are the advantages of Superheated Steam?

A

Dry steam for process equipment, more heat energy for great work output at same pressure

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16
Q

Where do air and gas mix in a High Pressure gas system?

A

in the Burner Register

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17
Q

What is the purpose of Duplex Strainers?

A

one can be cleaned while the other remains in service

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18
Q

What is the purpose of the Fuel Oil System?

A

supply fuel oil to the burner at the proper temperature and pressure

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19
Q

What fuel oil type must be heated?

A

Fuel Oil 6

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20
Q

Define Pulverized Coal

A

fine powder (talcum-like) blown into the combustion chamber and burned in suspension

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21
Q

Define Draft

A

flow of air or gases of combustion due to difference in pressure between two points

22
Q

Define Natural Draft

A

flow of gases caused by temperature difference between column of air inside the chimney as opposed to column outside the chimney

23
Q

What is Induced Draft?

A

air flow through pulling motion. Induced Fan in breeching between boiler and chimney pulling air through boiler furnace producing slight negative pressure in furnace

24
Q

Where is the Boiler Safety located?

A

highest part of the steam space of the boiler and on the Superheater header outlet (if present)

25
Q

Why are Safety Valves used?

A

to prevent the boiler from exceeding the MAWP

26
Q

How do Safety Valves function?

A

automatic, full-open, pop-action

27
Q

How much can the pressure exceed the MAWP before the Safety Valve opens?

A

Must be able to discharge steam without pressure increase over 6% above set pressure. Safety Blowdown is at least 2-8 psi below poping pressure, never to be lower than 4% of the set pressure

28
Q

How much of the total boiler set point pressure must be on the Safety Valve for a Manual Test?

A

75% of popping pressure

29
Q

Who repairs the Safety Valve?

A

Manufacturer’s Rep or Manufacturer

30
Q

What is the correction factor for Hydrostatic Pressure?

A

0.433 psi

31
Q

How does a Steam Separator work?

A

Internal drum in steam drum increases steam quality by changing flow direction, causing heavier water droplets to separate from steam

32
Q

When must Two Main Steam Stop Valves be used on a boiler?

A

ASME code: high pressure boilers in battery to common header with manhole openings and ample free-blowing drain between the stop valves

33
Q

What type of valve is the Main Stop?

A

OS and Y Gate, may use Automatic Nonreturn Valve for one closest to the boiler

34
Q

Why are OS and Y Gate Valves used for Stop Valves

A

Offer no restriction to steam flow and can easily determine position by looking at the stem

35
Q

What is the purpose of the Huddle Chamber in the Safety Valve?

A

increases surface area of safety valve Disc, which increases Total Force, causing the valve to open quickly (pop-open)

36
Q

When are two Bottom Blowdowns required?

A

Boiler at or above 100 psi (2 valves mounted on same line: both slow-opening, or one quick-opening and furthest slow-opening)

37
Q

Define Steam Quality

A

ratio of dry steam to total amount of water evaporated. Ex. 98% (98% steam, 2% water)

38
Q

What is necessary to protect Superheater tubes from overheating?

A

during boiler warm up, open superheater Drain and leave open to allow steam to constantly flow to reduce heat. When boiler 25% or higher of boiler capacity, then close drain

39
Q

What is the cause of Water Hammer?

A

mixing of steam and water

40
Q

What is a necessary component of a Steam Trap?

A

Inlet Strainer (prevents scale and solids entering)

41
Q

How does a Thermostatic Steam Trap operate?

A

Temperature operated element (bellows) filled with alcohol/water solution that boils at a few degrees below saturation temperature. More alcohol in solution increases sensitivity

42
Q

How does a Thermodynamic Steam Trap operate?

A

Single moveable disc rises to discharge air and cool condensate. Air or condensate enters inlet port under center of disc and lifts seat

43
Q

How are steam traps tested?

A

sight, sound, temperature, conductivity (temp crayons, thermometers, etc)

44
Q

What is NOWL?

A

Normal Operating Water Level

45
Q

What is the purpose of the Water Column?

A

to reduce turbulence in the water for a more accurate water level in the Gauge Glass

46
Q

What is the purpose of the Feedwater Regulator?

A

Maintain the water level in the boiler by controlling feedwater pumped in

47
Q

What is the fuel savings achieved through preheating feedwater?

A

for every 10 degrees increase in feedwater, 1% in fuel savings

48
Q

What is the consequence of too high of feedwater temperature?

A

Feedwater pumps can become steam bound

49
Q

What is the consequence of too low of feedwater temperature?

A

Thermal shock in the boiler

50
Q

What is the concept of the Turbine Feedwater Pump?

A

Rotary positive displacement with flat impeller and small perpendicular fins in impeller rim to discharge feedwater. Requires a relief valve on discharge

51
Q

What occurs when the Feedwater Heater water level is too low?

A

Oxygen can be sent to the boiler causing corrosion. Too low water pressure on suction side of pumps could cause cavitation

Boiler (2 decks)

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